Engineered "super-enzyme" gobbles plastic waste at six times the speed

Back in 2018, scientists in Japan made the key discovery of a bacterium with a natural appetite for PET plastics. This raised the prospect of a low-cost solution to some of the most common forms of plastic pollution, and now scientists have used this bacterium as the basis for a newly engineered “super-enzyme” that can digest plastic waste six times faster.

Known as Ideonella sakaiensis, the bacterium discovered by scientists at the Kyoto Institute of Technology a couple of years ago showed a remarkable ability to use PET plastics as its energy source. These are the materials used to construct everything from soda to shampoo bottles, with hundreds of millions of tons produced every year, and the team was excited to find that the bacterium could completely break it down within a matter of weeks.

The bacterium was found to do so through a pair of enzymes, one of which, called PETase, was soon engineered in the lab by researchers from the University of Portsmouth and the National Renewable Energy Laboratory (NREL) to be around 20 percent faster at breaking down plastic than it was originally. Now, the same team has succeeded in combining it with its partner enzyme, called MHETase, to up the digestion rate even further.

The scientists achieved this by first studying the atomic structure of the enzymes with a synchrotron that uses X-ray beams 10 billion times brighter than the Sun. This serves as a microscope, allowing the team to solve their 3D structure and use these insights to engineer connections between the two enzymes. Simply combining the two enzymes doubled the speed of the plastic digestion, but engineering special connections between them resulted in a “super enzyme” that again increased the rate of plastic degradation by another three times.

“Our first experiments showed that they did indeed work better together, so we decided to try to physically link them, like two Pac-men joined by a piece of string,” says the University of Portsmouth’s Professor John McGeehan, “It took a great deal of work on both sides of the Atlantic, but it was worth the effort – we were delighted to see that our new chimeric enzyme is up to three times faster than the naturally evolved separate enzymes, opening new avenues for further improvements.”

Just like its predecessors, as the new super-enzyme digests PET plastics it returns the material to its original building blocks, which means the technique could be used as part of an infinite recycling loop. The original enzyme couldn’t do this fast enough to account for the huge amounts of PET waste generated around the globe each year, so producing an engineered version that increases the rate six-fold is seen as a significant step forward.

The research was published in the journal Proceedings of the National Academy of Sciences of the United States of America.

Source: University of Portsmouth